Zeolites and zeolite-like materials are porous crystalline materials made of tetrahedral or octahedral oxide building blocks, linked together through tetrahedral or octahedral corner oxygen atoms. There are many ways in which the tetrahedral or octahedral building blocks may link to form polynuclear complex structures, having different topologies. In some structures, the building blocks link to form infinite chains, forming fibrous needle-like crystals. In other structures, the building blocks are linked in layers or sheets. In yet other structures, the building blocks are linked in three dimensions with mutual sharing of oxygen atoms, thereby forming a framework structure containing void spaces, such as channels (pores) and cavities. The chemical composition of zeolites and zeolite-like materials as well as the nature of the void space and the interconnecting channels are responsible for the catalytic and shape-selective properties of each zeolite or zeolite-like structure. Zeolites and zeolite-like materials can have channels that may or may not intersect with each other. When the channels intersect with each other, the channel intersections may form cavities within the crystal structure. Many natural and synthetic zeolites or zeolite-like materials with distinct crystal structures are currently known and are recognizable by distinct and characteristic X-ray diffraction patterns.
Zeolites and zeolite-type materials are used as sorbents and/or catalysts in many commercial processes, particularly in petroleum refining and petrochemical processes.
Typically, synthetic zeolite and zeolite-like molecular sieves are prepared by crystallization of an aqueous reaction mixture containing sources of the desired inorganic oxide building blocks and an organic structure directing (templating) agent, such as a nitrogen-containing compound. By varying the synthesis conditions, zeolite or zeolite-like structures of many kinds can be prepared. While each element of the synthesis may have an influence on the type of structure that crystallizes, the organic structure directing agent often plays an important role in defining the types and sizes of the channels and cavities in the resultant crystalline products. However, the type of crystal structure that might be obtained from a given synthesis mixture with any given organic structure directing agent is currently unpredictable. Many different kinds of amines and ammonium compounds have thus been reported to be suitable organic structure directing agents for various crystalline molecular sieve structures.
There is thus a continuing need to find new organic structure directing agents suitable for the synthesis of zeolites or zeolite-like materials.